The protozoan parasite Entamoeba histolytica causes amebiasis, which remains a major health problem in much of the world, and is considered a potential biological weapon. The two main forms of disease, amebic colitis and amebic liver abscess arise from complex interactions between the host and parasite. In the previous funding period, we focused primarily on the host, and established new paradigms about the role of inflammation and apoptosis in amebic disease. In this renewal we will return our focus to the parasite, and will look at what we have termed the amebic virulence program: E. histolytica molecules that must be expressed or suppressed to allow amebic invasion and survival within host tissues. We will define the virulence program through a transcriptional analysis, and ask how the virulence repertoire differs between amebic trophozoites in culture, those that have invaded into the colonic mucosa, and trophozoites within the liver. We will attempt to identify the requisite components of this response, and determine whether blocking their expression can alter the course of amebic colitis or amebic liver abscess. We will test the hypothesis that host macromolecules serve as triggers for the activation of the amebic virulence program, and test candidate amebic molecules for their role in recognizing host molecules and initiating the amebic virulence program: We will then determine whether blocking host macromolecule recognition, or signaling by amebic receptors, alters the course of amebic colitis. The above studies look at virulence in the context of amebic response to the host. We will also investigate the inherent virulence repertoire of E. histolytica HM1:IMSS by looking at differences at the transcriptional level between HM1:IMSS and the reduced virulence E. histolytica Rahman. When complete, these studies should provide new insights into the biology of E. histolytica, will further our understanding of the pathophysiology of amebic colitis and amebic liver abscess, and will identify new virulence factors that may play unique roles in amebic colitis or amebic liver abscess and could be targets for new vaccines or therapeutics. ERFORMANCE SITE(S) (organization,city,state) Washington University 660 South Euclid Avenue St. Louis, MO63110 PHS 398 (Rev. 09/04) Page 2 Form Page 2 Principal Investigator/Program Director (Last, First, Middle): Stanley, Samuel L, Jr. KEY PERSONNEL. See instructions. Use continuation pages as needed to provide the required information in the format shown below. Start with Principal Investigator. List all other key personnel in alphabetical order, last name first. Name eRA Commons User Name Organization Role on Project Samuel L. Stanley Jr. Stanleys Washington University Principal Investigator OTHER SIGNIFICANT CONTRIBUTORS Name Organization Role on Project Human Embryonic Stem Cells [X] No CH Yes If the proposed project Involves human embryonic stem cells, list below the registration number of the specific cell line(s) from the following list: http://stemcells.nih.gov/registrv/index.asp. Usecontinuation pages as needed. If a specific line cannot be referenced at this time, include a statement that one from the Registry will be used. Cell Line Disclosure Permission Statement Applicable to SBIR/STTR Only. See instructions, d Yes d No PHS 398 (Rev. 09/04) Page 3 Form Page 2-continued Number the followingpages consecutively throughout the application. Do not use suffixes such as 4a, 4b. Principal Investigator/Program Director (Last, First, Middle): Stanley, Samuel L. Jr. The name of the principal investigator/programdirector must be provided at the top of each printed page and each continuation page. RESEARCH GRANT TABLE OFCONTENTS Page Numbers Face Page 1 Description,